Reclaiming photographic film scrap



r'ai ented Jan. 10, 1939 UNITED STATES Exam PATENT OFFICE assignors, by mesne assignments, to

Eastman Kodak Company, Jersey City, N. J., a

corporation of New Jersey No Drawing. Application April 7, 1936, Serial No. 73,186

4 Claims.

This invention relates to the reclaiming of photographic film scrap and more particularly to a process for reclaiming scrap derived from film which has been colored or tinted with dyes for various purposes.

As is well known, photographic film base is tinted or dyed in order to obtain various effects. For example, in making Cine positive film which is to be used for showing fire scenes, the film is often tinted red in order that the simulation of the colors of such scenes may be as close to the actual as possible. In other cases, as where it is desired to simulate night scenes, especially scenes where moonlight efiects are desired, the film is tinted blue. In addition, various antihalation backings are employed with certain types of film. These tints are applied to the film from solution, generally a so-called subbing solution, containing solvents which penetrate considerably into the body of the film. In this manner, the dyes or tints are carried into the body of the film, sometimes penetrating as tnuch as or of the thickness of the film base.

In reclaiming tinted film scrap, extreme difficulty has been encountered in completely decolorizing the material. It has been found that the ordinary bleach liquors, even if employed under optimum conditions and for fairly considerable lengths of time, do not completely remove the last traces of tint from the recovered material. In order to reuse film scrap in'the manufacture of film and other products, it is of :paramount importance that the cellulose derivative material be absolutely colorless in order that a clear, water-white solution or dope -may be obtained when it is dissolved in appropriate -solvents.

The principal object of the present invention is to provide a step in the process of reclaiming photographic film whereby the material may be completely decolorized and the last traces of tint removed therefrom. Another object is to provide a process for decolorizing film scrap which is extremely simple and effective in its operation. Other objects will appear 'hereinafter.

These objects are accompanied by the following invention which, in its broader aspects comprises adding to the bleach liquor, customarily employed for decolorizing such material, an O1? ganic liquid which has the power of penetrating into the material and at the same time carrying the bleaching agent with it, thus enabling the bleaching agent to act upon and completely remove all traces of color, even though the dye or other coloring material may be located at considerable depth in the film material. In accordance with accepted practice, aqueous solutions of sodium, calcium or other hypochlorites are employed for bleaching tinted film, but since aqueous solutions cannot penetrate into the film base, because water will not wet cellulose derivative material, they are ineffective completely to remove the color therefrom. In carrying out experimental work on the use of these solutions, we found that the penetrating efiect of the bleach liquor could be greatly improved by adding thereto certain organic solvents which have the power of wetting, dissolving or swelling the cellulose derivative material, such as acetone or ethyl alcohol. However, these liquids were found to be unsatisfactory due to their susceptibility to oxidation or chlorination under the conditions prevailing in the bleach bath and the attendant formation of objectionable by-products. For example, acetone in the presence of chlorine forms various chlorinated products such as chloracetone, an extremely irritant compound sometimes used as a 'lacrimator in chemical warfare. Furthermore, acetone oxidizes in the presence of the bleach liquor to form chloroform and acetic acid. If ethyl alcohol is used, this is oxidized to acetaldehyde, and, in the presence of chlorine, forms chlorinated aldehydes and chloroform. It will thus be seen that, not only are such liquids the source of undesirable products in the bleach bath, but they tend to destroy the effectiveness of the bath by absorbing its active chlorine. After extensive work with these materials, We have found that methyl alcohol is unique in its power of penetrating the film material and its ability to withstand the action of chlorine under the conditions employed in the bleach bath. We have found, for example, that cellulose derivative film scrap can be completely decolorized, and in less than one-half the time usually required, when about 40% 'by weight methanol is added to the bleach liquor.

-In the following example and description we have set forth several of the preferred embodi- -ments of our invention, but they are included merely for purposes of illustration and not as a limitation thereof.

Our process will be more fully understood by reference to the following example:

250 lbs. of tinted cellulose nitrate photographic film scrap which has been washed in the usual way to remove the emulsion is added to a decolorizing bath consisting of 6000 lbs. of solution.

The solution is made up by adding 2400 lbs. methyl alcohol to 6000 lbs. of a calcium sodium hypochlorite bleach solution made up in the usual way. After adding the film support to the solution, carbon dioxide gas is bubbled into the agitating mass until the solution bleaches litmus paper readily. Then gas is bubbled into the solution at frequent intervals in order to keep the bleach solution active. When the color is sumciently reduced, the solution is withdrawn and the cellulose derivative material washed with several changes of water, after which it is dried and is then ready for redissolving to make film dope.

The composition of the bleach bath may vary rather widely, depending upon the particular cellulose derivative film scrap or other material dealt with. Although we prefer to employ sodium hypochlorite as the bleaching agent, other alkali metal, alkaline earth metal hypochlorites or chlorine water may be employed if desired. Likewise, the bath may be acidified with various acids such as carbon dioxide, acetic acid and others. Regardless of the composition of the bleach bath, in accordance with the present invention, methanol is added thereto in an amount representing approximately 40% by weight of the liquid. The percentage of methanol added may also be varied within rather wide limits, although I prefer to use a fairly high percentage, such as 30, 40 or even 50%. In general, it may be said that the higher the concentration of methanol the more readily can the bleaching action be accomplished. However, too high a concentration of methanol is undesirable because of excessive solvent action on the cellulose derivative material of the film, particularly in the case of cellulose nitrate film.

Although we have described our invention by reference to cellulose nitrate film tinted with a particular type of dye, it will be evident that our process is broadly applicable to the treatment of any type of tinted cellulose derivative film base colored with any type of dye or coloring matter susceptible of decolorization by oxidation under the conditions existing in the bleach baths ordinarily employed in the reclamation of photographic film.

One of the distinguishing features of our invention is that, by the use of methanol as herein described, we are enabled to obtain the full bleaching effect of the bleach liquor. In other words, the action of the methanol is to penetrate well into the cellulose derivative material, swell and, in a sense, open it up in such a way as to permit permeation by the bleach liquor. In this way the full oxidizing action of the bleach on the dye can be obtained, even though the color has deeply penetrated the film in some cases as much as 20-30% of the thickness of the material. When film scrap decolorized in this manner is dissolved in appropriate solvents, a perfectly clear, water-white solution or dope is obtained which may be reused in the manufacture of photographic film or other products.

Not only is it possible to obtain a perfectly decolorized film scrap by our process, but the time of bleaching is also materially cut down. For example, where it has heretofore been necessary to bleach the film for a period of 90 minutes,

the use of methanol in accordance with our in vention cuts this time to minutes or less.

Although we have described our invention by reference to a process involving the decolorizing of film scrap composed of cellulose nitrate, it will, of course, be understood that our process is broadly applicable to decolorizing of photographic film or other sheet material composed of any of the cellulose derivatives and containing a dye or tint. For example, the process herein described may be employed effectively to decolorize film or sheeting composed of the organic acid esters of cellulose such as cellulose acetate, cellulose propionate, cellulose butyrate or the mixed organic acid esters of cellulose such as cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate stearate and the like. In the case of the organic acid esters of cellulose, although methyl alcohol is not strictly solvent with respect thereto, it nevertheless exerts a penetrating and swelling action which brings the cellulose derivative material into a condition in which the bleach bath can readily penetrate it and exercise its oxidizing action on the dyestuif which it may contain. It will, of course, also be apparent that our invention is applicable to the decolorizing of film or sheeting which has been produced from a colored dope as distinguished from a product which has been colored merely by the application of a tinted subbing solution thereto.

What we claim is:

l. The process of decolorizing tinted cellulose ester photographic film scrap containing a dye which has penetrated well below the surface thereof and is entrained in the subsurface layers thereof, which comprises subjecting the material in its original condition to the action of a bleach bathcomprising an aqueous solution of sodium hypochlorite containing not over about based on the weight of the original bath, of

methanol.

2. The process of decolorizing tinted cellulose derivative scrap containing a dye which has penetrated well below the surface and is entrained in the subsurface layers thereof, which comprises subjecting the scrap in its original physical condition to the action of a bleaching bath containing a chlorinated bleaching agent and methanol.

3. The process of decolorizing tinted cellulose derivative photographic film scrap containing a dye which has penetrated well below the surface thereof and is entrained in the subsurface layers thereof, which comprises subjecting the scrap in its original physical condition to the action of an aqueous hypochlorite bleach bath containing methanol.

4. The process of decolorizing tinted cellulose ester photographic film scrap containing a dye which has penetrated well below the surface thereof and is entrained in the subsurface layers thereof, which comprises subjecting the scrap in its original physical condition to the action of a bleach bath comprising an aqueous solution of sodium hypochlorite containing approximately 40%, based on the weight of the original bath, of methanol.

GALE F. NADEAU. MARVIN J. RED). 

